I prove some theorems for competitive equilibria in the presence of distortionary taxes and other restraints of trade, and use those theorems to motivate an algorithm for (exactly) computing and empirically evaluating competitive equilibria in dynamic economies. Although its economics is relatively sophisticated, the algorithm is so computationally economical that it can be implemented with a few lines in a spreadsheet. Although a competitive equilibrium models interactions between all sectors, all consumer types, and all time periods, I show how my algorithm permits separate empirical evaluation of these pieces of the model and hence is practical even when very little data is available. For similar reasons, these evaluations are not particularly sensitive to how data is partitioned into "trends" and "cycles." I then compute a real business cycle model with distortionary taxes that fits aggregate U.S. time series for the period 1929-50 and conclude that, if it is to explain aggregate behavior during the period, government policy must have heavily taxed labor income during the Great Depression and lightly taxed it during the war. In other words, the challenge for the competitive equilibrium approach is not so much why output might change over time, but why the marginal product of labor and the marginal value of leisure diverged so much and why that wedge persisted so long. In this sense, explaining aggregate behavior during the period has been reduced to a public finance question - were actual government policies distorting behavior in the same direction and magnitude as government policies in the model?

We analyze the Italian economy in the interwar years. In Italy, as in many other countries, the years immmediately after 1929 were characterized by a major slowdown in economic activity as non farm output declined almost 12. We argue that the slowdown cannot be explained solely by productivity shocks and that other factors must have contributed to the depth and duration of the the 1929 crisis. We present a model in which trade restrictions together with wage rigidities produce a slowdown in economic activity that is consistent with the one observed in the data. The model is also consistent with evidence from sectorial disaggregated data. Our model predicts that trade restrictions can account for about 3/4 of the observed slowdown while wage rigidity (monetary shocks) can account for the remaining fourth.